Lubricating oil compositions containing bi-metal dithiophosphates



LUBRICATING OIL COMPOSITIONS CONTAINING BI-METAL DITHIOPHOSPHATESJames-H. Walker, Richmond, Calif., assignor to California ResearchCorporation, San Francisco, Calif., a corporation of Delaware NoDrawing. Filed Dec. 31, 1956, Ser. No. 631,464 3 Claims. (Cl. 252-325This invention :pertains to lubricating oil compositions which areparticularly beneficial to use where silver wearing surfaces areconcerned.v

In particular, lubricating oil compositions of. thisinvention areresistant to oxidation .and noncorrosive to silver wearing surfaces, aswell as to the conventional metal alloy surfaces. Such lubricating oilcompositions contain particular bi-metal saltsof dithiophosphoric acids.

Generally, oils of lubricating viscosity are now subjected to highertemperatures and greater conditions of wear than those whichvexistedonly a relatively few years ago. Such changes in lubricatingrequirements are due primarily to the many advances which have occurredin the design of automotive equipment. For example, diesel engines usedin railway service arenow equipped with bearings lined with pure silvermetal. Also, many auto- United States Patent lice 2,945,810 PatentedJuly .19, 1960 Thus, the oxidation and silver corrosion resistantoilcompure silver.

By the use of the particular bi-metal dithiophosphates of thisinvention, oxidation-resistant lubricants noncor- Iosive to silver havebeen obtained. The "particular reasons underlying the effectiveness ofthese particular dithiophosphates herein as inhibitors for lubricatingoil compositions. is .not :known'.

'As used herein, the .term' bi-metal salts :of .dithiophos tpjhoricacids means :the product which is obtained by reacting'an:al'kaline'earth metal oxide or hydroxide with a metal salt of an esterof dithiophosphoric acid, the

metals being dissimilar.

The metal salts of esters of dithiophosp'horic acids of the prior'artwhich .r'eact withalkaline earth metal oxides mobiles have valve lifterswhich are subject to such high loads that the bearing surfaces operateunder conditions approaching boundary lubrication. Thus, newrequirements have been imposedonlubricating oils so that oils which weresatisfactoryjust a few years ago are now inadequate for properlubrication.

Metal salts of thiophosphoric acids, particularly alkaline earth metaland zinc salts of alkyl or alk'ylaryl dithiophosphoric acids, have longbeen used as additives for lubricating oils. These salts have beenextremely efiective in inhibiting oxidation of oils and corrosion ofalloy bearings. In more recent years, dithiophosphate salts were foundto have another useful property, that of imparting extreme-pressureproperties to oils. Because of these favorable characteristics,dithiophosphate salts have been outstanding among lubricating oiladditives.

Even though the salts .of dithiophosphoric acids have such virtues aslisted hereinabove, these salts have not been used universally becauseof one serious drawback; that is, such salts cause severe corrosion ofsilver in engines employing silver wearing surfaces. This attack ofsilver is believed due to the sulfur of the dithiophosphates. Thissulfur attack on silver has often, been so severe in railroad dieselengines as to render these engines unfit for service after acomparatively short period of operation. In attempts to take advantageof the oxidation and corrosion inhibiting properties of thethiophosphate salts, the petroleum industry has spenta great deal ofeffort to overcome the deficiency with regard to silver. Although silverprotective agents have been developed to minimize this sulfur attack bythe thiophosphate salts,

isueh additives have not beenentirely satisfactory.

and hydroxides to :form the new bi-metal basic dithiophosphates hereinare represented by the following formula:

RO-P-s- M droxidereactants, used in the formation of :the bi-metaldithiophosphates. At least one of the metals of the -bimetaldithiophospha-tes is an alkaline earth metal.

The R radicals and the R radicals can be derived from straight chain orbranched chain alcohols containing at least 8 carbon atoms, .oralkylphenols wherein the alkyl radicals .contain a total of at least 6carbon atoms; for example, n-octanol, Z-ethylhexanol, 2-propylpentanol,decanol, undecanol, vdodecanol, hexadecanol, octadecanol,vdipropylphenol, hexylphenol, dibutylphenol, decylpheno'l,dodeeylphenol, hexadecylphenol, octadecylphenol, dioctylphenol,2-phenylhexanol, etc.

Examples of esters of dithiophosphon'c acids which are reacted with thealkaline earth metal oxides or hydroxides are dioctyl dithiophosphoricacid; octyldecyl dithiophosphoric acid; didecyl dithiophosphoric acid;didodecyl di-th iophosphorio acidydihexadecyl dithiophosphoric acid;dioctadecyl dithiophosphoric acid; di(decylphenyl) dithiophosphoricacid; di(am-ylphenyl)- di-thiophosphoric acid; di (dodecylphenyl)d-ithiophosphoric acid, etc.

Improved oil solubility of the resulting bi-metal dithiophosphate isobtained when the alkaline earth metal oxide (or hydroxide) reactant isa barium oxide (or hydroxide), the metal salt of dithiophosphoric acidis a zinc salt of esters of dithiophosphoric acid, and wherein each ofthe ester radicals (i.e., the R and R of the formula hereinabove) arederived from alcohols or alkylphenols containing not less than 12,carbon atoms, and not more than 25 carbon atoms (i.e., it is preferredthat the total number of carbon atoms in the ester radicals-is 24 to50).

M is a metal For purposes of simplification, the metal of the alkalineearth metal oxide and hydroxide reactants will be termed secondarymetal, and the metal of the. dithiophosphate reactant will be termedprimary dithiophos phate metal. 7

The particular bi-metal salts of esters of dithiophosphoric acids withwhich I am concerned have molecular weights of such magnitude as toindicate the formation 'of complex polymeric type compounds. Molecularweight data for these compounds, as determined by sedimentation rates inan ultracentrifuge, show that the molecular Weights are in the range of150,000 to 550,000.

Suitable base oils include a wide variety of lubricating oils such asnaphthenic base, paraffin base, and mixed base mineral oils; syntheticoils, e.g., alkylene polymers, such as polymers of propylene, butylene,etc., and mixtures thereof; alkylene oxide type polymers; dicarboxylicacid esters; liquid esters of phosphorus and silicon; and alkyl aromatichydfocarbdns;

The above base oils may be used individually as such or in variouscombinations (wherever miscible or whenever made so by the use of mutualsolvents).

The bi-metal salts of esters of dithiophosphoric acids are used inlubricating oils in amounts sufliicient to inhibit oxidation thereof;that is, amounts of 0.25% to 20%, by weight, preferably from 1.5% to 10%by Weight. Stated in other terms, the amounts of these bi-metaldithiophosphates may be expressed as millimols per kilogram" of finishedoil, based on the phosphorus content. That is, the amountof bi-metaldithiophosphate is ex- Expressed in such terms, the amount of bi-metalsalts of esters of dithiophosphoric acids used in lubricating oils canbe from 1 millimol to 50 millimols of phosphorus per kilogram offinished oil, preferably from 4 millimols to 25 millimols.

In the preparation of the bi-metal salts of esters of dithiophosphoricacids, the simple neutral metal salts of esters of dithiophosphoricacids of the prior art can be prepared by methods known heretofore. Forexample, a mixture of the desired alcohol or alkylphenol and phosphoruspentasulfide is reacted with or without a solvent (e.g., petroleumnaphtha) at 100 F. to 200 F. until the dithiophosphoric acid is formed.The crude acid mixture is then filtered to remove unreacted phosphoruspentasulfide, after which the resulting acid is neutralized with a metaloxide (e.g., zinc oxide) to form the metal dithiophosphate. Such simplemetal salts of esters of dithiophosphoric acids can also be prepared byreacting the dithiophosphoric acid with sodium hydroxide to form thesodium salt, then precipitating the desired metal salt from a solutionof the sodium salt by the addition of a metal chloride (e.g., zincchloride or calcium chloride).

The bi-metal salts of esters of dithiophosphoric acids (e.g.,barium-zinc diester dithiophosphates) are prepared by reacting a metaldiester dithiophosphate with an alkaline earth metal oxide (orhydroxide) in a solvent (e.g., a lubricating oil), followed by heatingto a temperature ranging from 200 F. to 450 F. (preferably from 250 F.to 375 F.), and filtering the resulting admixture. The followingexamples illustrate the preparation of lubricating oil compositions ofthis invention.

EXAMPLE 1 A mixture of 5 pounds (0.032 pound mol) of barium oxide (92%purity) and 125 pounds (0.0625 pound mol) of a zinc di(alkylphenyl)dithiophosphate (wherein the alkyl radical is derived from propylenepolymers having an average of 12 carbon atoms) containing 3.27% zinc,3.0% phosphorus, and 5.78% sulfur, was incorporated in a Californiasolvent-refined paraflin base oil having a viscosity of about 140 SSU at100 F. The whole mixture was heated in a kettle with agitation at300-310 F. for a period of 1.4 hours. 79 pounds (0.245 pound mol) ofbarium hydroxide octahydrate (98% purity) was then .pressed as millimolsof phosphorus per kilogram of oil.

as silver corrosion inhibitors.

'2,945,s1o p I e v acharged at the rate of 20 pounds per hour while thetemperature was maintained at 300 F. to 310 F. The barium to-zinc molratio of this charge was 4.43 to 1.0. The pH of the charge (determinedin a solvent consisting of 40%, by volume, of ethyl alcohol; 40% ethylether; and 20% water) increased from 4 to 13+. The whole mixture wasagitated at 300 F. for another hour, with nitrogen flowing through thebottom of the kettle to remove residual moisture. This was followed by afinal drying period of 30 minutes at 300 F. under a vacuum of 25 inchesof mercury. To this mixture was added 5 pounds of Celite filter aid,after which the mixture was cooled to 250 F. and filtered.

The resulting product analyzed 1.76% zinc, 16.73% barium, 1.63%phosphorus, and 3.26% sulfur. The mol ratios based on zinc, as one, wereas follows: barium, 4.52; phosphorus, 1.95; and sulfur, 3.78. Theviscosity was 3838 SSU at F., and SSU at 210 F.

The barium-Zinc dialkylphenyl dithiophosphate product thus formed Wasisolated from the lubricating oil concentrate as follows: 100 grams of alubricating oil solution of the concentrate was dissolved in 100 ml. ofbenzene. 300 ml. of CP acetone was added to precipitate out thecompound. The solid fraction precipitating out was separated andredissolved in 100 ml. of benzene and reprecipitated with 300 ml. of CPacetone.

Table I hereinbelow sets forth the analysis of the reprecipitated solid,again using the zinc content as the base for determining the molratio.

Table II hereinbelow presents data showing the effectiveness of thebi-metal dithiophosphates of this invention The silver strip test whichwas used is described as follows:

A silver metal strip having the dimensions of 2 /2 inches by inch byinch was first cleaned with a wire brush until the strip was highlypolished. The strip was weighed and the weight recorded. This highlypolished silver strip was then placed in a 600 ml. beaker in such amanner that the strip was completely immersed when 300 grams of the oilbeing tested was poured into the beaker. The oil was stirred at atemperature of 300 F. for 20 hours, at which time the silver strip wasremoved and cleaned, first with chloroform, then with petroleum ether.The appearance of the strip was noted. Those strips which had beenseverely attacked were quite black. The tested silver strip was washedin 15% aqueous solution of potassium cyanide for about 5 minutes toremove the sulfide film adhering to the strip. After the strip had beenwashed with potassium cyanide and dried, it was weighed. The differencein weight of the original strip and the strip after the potassiumcyanide wash was noted and recorded as the weight loss due to corrosion.

The base oil of the compositions was a 60 V1. SAE 30 California baseoil.

The amounts of the several components of the oil compositions are setforth in terms of millimols of additive per kilogram of finished oil, asdetermined by the metal content. For example, when a calcium sulfonateis expressed as being present in an amount of 10 millimols per kilogram,it is meant that the sulfonate was present in such an amount that thecalcium content was 10 millimols per kilogram of finished oil.

ml. of test oil contained in a 400 ml. beaker.

Table II Tabllll" Gomponents/mM./kg. Oil N o.- 1 Oil No. 2 Additive(mM./kg.) StripqCozroston V 6S 3 M01 Base 011: 5 Ratio, CalciumPetroleum Sultnate 7 7 No Barium/ Copper- Suliurired OalcrumAlkylphenatel6 16 Zinc Bi-metal Sul- Phe- Lead Strip Silver Zinc Di(al kylphenyl)Dithiophosphate .4.... 6 Dithio fonate nafe- Strip Barium-Zinc-BasieDi(alkylphenyl) Dithiophosphate 1 phosphate u 1 3 ''6 A B Silver StripLoss, mgs 145 r 1.11 e 7 is. T as so 1 The alkyl radicals contained anaverage of 12 carbon atoms. 3.0 6 7 13. 0 2 67 1 6 mM./kg. as determinedby the zinc present. 3. 7 1 0.5 104 I 3; v 10 4' 8,1 1 Thus,.1t isreadily seen thatlubricatmg o1l compos1t1ons 4.1 6 7 i 16 1L8 7 Y 4.1 107 4;? L5 6:]. contalmng small amounts of bi-metal salts of.d1esters of 110 7 72 5 5 dithiophosphoric acids are practically non-corrosive to I 22j 6 4 4' 5 7 7 9' 107 8 43 s1 ver. 4. 5 1o 9 10 12" Y 6 Table IIIherembelow presents further data. showing 23 11 1 8 V 4. 5 12 7 15 7 theefiectiveness of bi-metal dithiophosphates as oxidation 10 4 i 37 v 5inhibitors and as silver corrosion inhibitors in lubricating oilcompositions.

The base oil, the test conditions, etc., which were used are describedas follows:

With-'the'exception of Examples 1 and 2 (wherein the base oil was SAEthe base-oil in each instance was a 60'V.I. SAE California base: oil.

The bi-metal dithiophosphates were prepared (unless otherwise noted)according to the process described in Examplel hereinabove, by reactingbarium oxide and barium hydroxide. with a zinc di(alkylphenyl-)dithiophosphate, wherein the alkyl radical was obtained frompolypropylenes containingan average of 1-2 carbon atoms.

The sulfonate was a calcium petroleum sulfonate wherein the petroleumradical was obtained from a California paraifin base oil having aviscosity of 480 SSU at: 100 F.

The. phenate was asulfurized calcium alkylphenate wherein the alkylradical was obtained. frompolypropylenes having an average of 12 carbonatoms.

The copper-lead strip corrosion test A was run as follows: A polishedcopper-lead strip (obtained from a commercial bearing) was weighed andimmersed in 300 The test oil wasmaintained at 295 F. under a pressure ofone atmosphere of air and vigorously stirred with a mechanical stirrer.After 2 hours, a catalyst was added to provide the following. catalyticmetals (all percentages being by weight):

The test was continued for 20 hours, after which the copper-lead stripwas removed, rubbedvigorously with a soft: cloth, and weighed to.determine the weight loss. The copper-lead corrosion strip test- B wasrun as follows: A polished copper-lead strip (obtained from a commercialbearing) was weighed and immersed in 300 ml. of test oil contained in a400 ml. beaker. The test oil was maintained at 340 F. under a pressureof one atmosphere of air and vigorously stirred with a mechanicalstirrer. After 2 hours, the following catalyst was added to provide thefollowing catalytic metals (all per centages being by weight):

The test was continued for 20 hours, after which the copper-lead stripwas removed, rubbed vigorously with a soft cloth, and weighed todetermine the net weight loss.

- lirepared frombarium oxide onl'y. 0.1% of asulturizeddiparaflfinsulfide. As noted from the above data, the -bi-metal' dithioa phosphatesare particularly efiective. aslubricating oil additives; when the mol:ratio of the secondary metal to the. primary dithiophosphate metal is.from about 3.7 to 1 to about 4:6 to 1 (=i:e.,.ha's:avaluefrom13;7 to4.6); TableIV hereinbelow sets-forth data obtained ina the ChevroletL-.-4 engine test, further show-ingthe effectivenessofthe-bi-metal basicsalts of diesters of dithiophosphoric' acids. as oxidation-corrosioninhibitors.

In.the L-4 engine test, corrosion characteristics of: the oilzweredetermined :ina; Chevrolet standardo-cylinder enginein atypicallaboratoryinstallation. Weighed copperlead test. bearings and newpiston rings. were installed. The test was run at a constant enginespeed of 3150 r.p.m. under a load of 30 brake horsepower for a total of36 hours subsequent to a run-in period of 8 hours. The

outlet temperature of the jacket coolant was 200 F: and the oil sumptemperature was 280 F. At the conclusion of the test, the engine wasdisassembled and inspected for varnish and sludge deposits,. and thevarious parts were rated on a cleanliness scaleof 0. to 10,. 10 beingperfectly clean. The bearings were weighed to determine the weight lossper whole bearing due to cor rosion. This L-4 engine test is more fullydescribed in the CRC Handbook, 1946 edition, Coordinating ResearchCouncil, New York, N.Y.

compounded oil (A) was a 60 V1. SAE 30' California (base oil containing7 mM./kg. of neutral calcium petroleum sulfonate and 0.1% by weight of asulfurized diparaflin. sulfide.

Table. IV

Oil. I Weight Loss,.mg.

' per Whole Bearing (1) (;A) Greaterthan-500'. (2) Oil (A)+l0 mM./kg.Barium-zinc Di(alky1- .50.

phenyl) Dithiophosphatc.

1 The alkyl radicals were derived from polypropylenes containing anaverage of 12 carbon atoms. The barium/zine mol ratio was 4.4/1.

Table V hereinbelow presents data obtained from a test wherein the oilwas subjected to severe conditions of operation. These data wereobtained by the Navy Propulsion Load Tes-t described in MIL-P-17273(Ships, 15 July 1952). The tests were run in a General Motors 4-cylinderdiesel engine using 1% sulfur fuel. Copperlead bearings and pure silverbearings were employed. The tests were run at a constant speed of 1800r.p.m. under a load of 30 brake horsepower per cylinder for 300 hours.The crankcase temperature was maintained at 250 F. The test was runcontinuously to simulate railroad diesel engine performance, unlike the.standard Navy test procedure, which permits regular four-hour shutdownperiods. Sea water was also excluded for the Table V Weight Loss Copper-Oil Lead Bearing, mg. per Whole Hearing (2) Oil (A)+12 mM./kg.Barium-Zinc Di (alkylphenyl) Dithiophosphate Greater than 2,500. 11.

1 The aikyl radicals were derived from polypropylenes containing anaverage of 12 carbon atoms. The barium/7.11.10 mol ratio was 4.5/1.

The oxidation stability of the oils compounded with the bi-metal diesterdithiophosphates of the present invention was determined by thefollowing procedure. Oxidation tests were carried out in an apparatus ofthe type described by Dornte in Industrial & Engineering Chemistry, vol.28, p. 26 (1936). Oxygen at atmospheric pressure was passed through theoil, maintained at 340 F., a fine fritted glass filter being employed inthe bottom of the absorption cell to disperse the gas stream into veryfine bubbles. The amount of oxygen absorbed was measured, and the timein hours required for 100 grams of oil to absorb 1200 cc.- of oxygen(S.T.P.) called the induction period, was noted. These test data arereported in Table VI, hereinbelow, wherein the compounded oil (B) is a60 V.I. SAE 30 California base oil containing 7 mM./kg. calciumpetroleum sulfonate and 0.25% by weight of a sulfurized diparaffinsulfide. In order to compare the two oils in the table below atapproximately the same base level, a calcium salt of an alkylphenol wasadded to the oil containing the conventional zinc thiophosphate.

Table VI Induction Oil Period (Hours) (1) (EH-6 mM./kg. ZincDi(alkylphenyl) Dithiophosphate +1G mMJkg. of a Calcium Alkylphenate 2.5 (2) (EH-6 mM./kg. basic Barium-Zinc Di(alky1phenyl) Dlthiophosphate5.6

1 Alkyl radicals derived from polypropylene having an average of 12carbon atoms.

i Barium-to-zlnc mol ratio 4.1/1.

a Allryl radical derived from propylene polymers having an average of 12carbon atoms. 7

Although the compositions of the present invention have been describedabove as being primarily useful as internal combustion enginelubricants, the additives herein are suitable for use in gearlubricants, ice machine oils, instrument oils, constituent oils forgrease manufacture, turbine oils, and the like.

In addition to the additives noted hereinabove, the lubricating oils ofthis invention may contain other oxidation inhibitors, grease thickeningagents, color correctors, extreme pressure agents, oiliness agents, gelmodifiers, etc.

I claim:

1. A lubricating oil composition comprising a major proportion of amineral lubricating oil, and from about 0.25% to about 20%, by weight,of a bi-metal salt of a dithiophosphoric acid, wherein said bi-metalsalt is prepared by reacting barium oxide with a zinc salt of a diesterof dithiophosphoric acid of the formula:

wherein R and R are hydrocarbon radicals containing a total of from 12to carbon atoms, wherein the mol ratio of said barium to said zinc has avalue from 3.9 to 4.6, said bi-metal salt having a molecular weight inthe range of 150,000 to 550,000.

2. The lubricating oil composition of claim 1, wherein R and R arealkylphenyl radicals, wherein said alkyl radicals are derived frompolypropylenes having an average of 12 carbon atoms.

3. A lubricating oil composition comprising a major proportion of amineral lubricating oil, and from about 1.5% to about 10%, by weight, ofa bi-metal salt of a dithiophosphoric acid, wherein said bi-metal saltis prepared by reacting barium oxide with a zinc salt of a diester ofdithiophosphoric acid of the formula:

i Ro-r-S- Zn wherein R and R are alkylphenyl radicals having alkylradicals derived from polypropylenes having an average of 12 carbonatoms, wherein the mol ratio of said barium to said zinc has a valuefrom 3.9 to 4.6, and said bi-metal salt has a molecular weight in therange of 150,000 to 550,000.

References Cited in the file of this patent UNITED STATES PATENTS2,441,587 Musselman May 18, 1948 2,713,557 Lowe July 19, 1955 FOREIGNPATENTS 717,039 Great Britain Oct. 20, 1954 723,133 Great Britain Feb.2, 1955

1. A LUBRICATING OIL COMPRISING A MAJOR PROPORTION OF A MINERALLUBRICATING OIL, AND FROM ABOUT 0.25% TO ABOUT 20%, BY WEIGHT, OF ABI-METAL SALT OF A DITHIOPHOSPHORIC ACID, WHEREIN SAID BI-METAL SALT ISPREPARED BY REACTING BARIU, OXIDE WITH A ZINC SALT OF A DIESTER OFDITHIOPHOSPHORIC ACID OF THE FORMULA: